Just got my latest issue of "Greenhouse IPM Notes" from Rutgers and Cornell Cooperative Extension, and there’s an interesting article about a recent study by Raymond Cloyd at U. of Illinois at Urbana that determined that media treated with horticultural diatomaceous earth did NOT show any significant differences in fungus gnat survival when compared with the same media under the same growing conditions that contained no such treatment. This applied to three different concentrations of DE and to two different larval stages (2nd and 3rd larval instars). More work will be done to evaluate the product’s efficacy on the 1st instar larvae to see whether or not this stage might be more susceptible than more advanced stages of the fungus gnat larvae.

It’s interesting that lots of folks swear by this stuff as a gnat-suppressing agent...now the research seems to indicate that some other factor must be at work when anecdotal "evidence" is given by users as to its ability to reduce and/or eliminate gnat larvae in interiorscape plants.

For now, I’ll continue to go with Talstar GH, Decathlon or Marathon as quick-knockdown agents to swiftly reduce larval populations, followed by beneficial nematodes (Scanmask, etc.) for long-term control.

Clem

I’m one who swears by it. I do use Planter Technology subirrigation in every account I have ...... the 6" material though .. if anything .. will be the one to get the gnats, so anything I plant in 6" gets a top layer of a mixture of sand and DE ..... on the soil, under the moss. No gnats.

I am opting out of a contract with a PITA (Pain In The A--) client because they swear that bugs are biting them. I find ZERO evidence of any type of bug in the plants ...... no Tech has complained of getting bit. I keep explaining to them that bugs that bite people are for the most part not plant bugs. I have also offered (at my expense) that if they can find one and put it in an envelope for me that I would take it to UC Davis and see exactly what it is. Nothing. At this point I am considering the source .... some people just like to complain. I don’t need clients that bad to have one I can’t stand. Next !!!!!

Have a great weekend.

Debbie

I am wondering whether the study referred to above mixed the Diatomaceous earth in with the soil or placed it on top of the soil. I believe that if a layer (.5 - 1 inch)is placed on top of the soil that the fungus gnats will not survive crawling out of the soil. It has to be packed down somewhat.
Rick W.

I tried diatomaceuos earth on one account back when I was pregnant with my son (we took a zero-exposure, zero chance approach, so my co-workers were great in supporting that and coming out to my accounts to do my spraying for me.) I found that the diatomaceous earth helped, but did not eradicate. I think there are some variances maybe for how thickly you use spread these types of non-chemical controls, etc., but I for one was glad to hear about the same information Clem mentioned at Suzanne Wainwright’s presentation yesterday. That way, I’m not the only one with that experience!

Debbie, what kind of moss do you use? Spanish moss? Spanish moss can carry chiggers and some others I think that will bite. Would be interesting to ask an entomologist about your experience. Personally, I have walked away with a slight chigger-like itch on occasion from some accounts. Could be my skin was just reacting to an irritant, but it always made me wonder.

Yes, and thrips on dish garden plants are also a source of plant pests that will also bite people...all of us have seen thrips on the nephthytis, pothos, ardisia, dracaena and other dish garden denizens that populate the cubicles of America’s offices, and they could be the culprits, not just the professionally-supplied plants from interiorscapers.

We also are hearing a lot about bedbugs being a real problem in hotels especially, and who spends a lot of time in hotels around the world? Corporate execs, that’s who. They could be bringing these critters back in their luggage and infesting office furniture unwittingly.

Another possibility is fleas...a "cat lady" or other pet lover who has a less-than-exemplary sanitation record with their animals at home may be bringing in hitchhikers to the office...from one person’s clothing, the fleas can certainly spread throughout the workspace, biting and breeding with abandon. And the fleas will be somewhat more difficult to detect than flying insects due to their small size and ability to spring long distances when threatened with discovery.

Makes you want to take a desk job, doesn’t it?

Clem

I never found diatomaceous earth to do much good.

Nematodes are the way to go for taking care of fungus gnats.

One small containter is enough to do several accounts versus hauling around bags of the diatomaceous earth. That stuff is quite messy.

Our problems with gnats are few and far between these days. Whenever we do get a complaint, we just go in and put a tablespoon of nematodes into the soil of each plant and the problem dissapears.

We do do preventitive applications of acounts that had serious infestations and on important accounts where we don’t want to have problems.

The nematodes are easy to store, you can keep them up to 6 months.

I find them very cost effectice too.

The nematodes work so well I can’t understand why anybody would use anything else.

JK

you can find more info at:

www.greenmethods.com

You guys are making me itch !!! Yikes.

I have never heard of chiggers in California. I have also never seen a thrips in an interior setting here. Neither my Techs nor I have been bitten on this account ..... and you would think if this mystery biter is from the plants that we would have been.

I used to use nematodes when I first started out and was doing weekly watering ...... but I don’t believe nematodes work so well in subirrigation because the top few inches of soil stays dry.

When I use the sand/diatomaceous earth mixture I use about 1/4" completely covering the soil.

I use the Mr. Big moss that I get from Sunborne and I love it.

As for the flea thing ....... I moved into a ranch that had a basement a few years ago and my kids found a kitten who had fallen thru the dryer vent and when my daughter brought that thing upstairs fleas came out all over her shirt. We had no carpeting, only hardwood floors and tile thruought the place. I bombed the house twice and finally had to get an exterminator ..... and it took them three weeks to get rid of them. It was horrible. They loved my son and I ... we would cover ourselves in tea tree oil at night. My kids currently have two cats and they get bathed once a month and I use Frontline on them religiously. Fleas are gross.

Have a great week.

Debbie

Debbie, any drench, whatever the active ingredient, is probably not effective in CWI irrigation. You would have had to apply the drench in a top-watering manner for that one week to achieve control.

Is Mr. Big Moss an organic or synthetic product? Sorry, I am not familiar with that name brand.

Fleas are gross. That’s an aweful story, but it definitely happens. Fleas will also come in on socks, etc, and then lie dormant in carpet for months until triggered to hatch. Its not exactly an epidemic, but it happens.

Oh, I should have asked the first time- the bites your client is experiencing. What do they look like? A rash? A welt? Red mark? Any one particular part of the body? If you do get the chance to investigate further, that information will be helpful, too.

Just FYI, I got a nice reply from Dr. Ray Cloyd to an e-mail I sent him yesterday requesting his thoughts on the diatomaceous earth discussion here...he did say that the research he performed involved DE incorporated into the growing media, and that he attributes its failure to show significant benefits relates to the DE being wet from irrigation of the mix. He suspects that a layer of dry DE applied to the surface of the medium would work pretty well in controlling the emergence of adult fungus gnats, especially if the DE could be kept dry.

We all know intuitively that this would only work in subirrigated plants that do not have water poured over the surface of the medium...CWI systems come to mind. Once watered into the mix, the DE would become virtually useless for gnat control, since it does not have an effect on the sub-surface larval and pupal stages of the insect, as Dr. Cloyd’s research demonstrates. It would also lose much of its efficacy on emerging adults if it were wet, and don’t forget that top-watering of the DE would move much, if not all, of it off the surface and into the mix, where its value would be lost.

The key seems to be to maintain an undisturbed blanket of DE on the soil surface and to exclusively subirrigate in order to avoid having to continually re-apply it.

As has been pointed out by others as well as myself, the gnat-specific, beneficial nematodes are the way to go here.

Clem

I spoke with Donald Sturniolo, CEO of BioControl Systems while at TPIE. During the course of discussing the efficacy of nematodes toward fungus gnats, he stated that the nematodes needed to be re-applied. I found that interesting given that I’ve only ever heard very good feedback in regard to nematode use in an interiorscape setting. Has anyone else experienced this?

Clem,
That’s why I used the dio/sand on top of the soil ...... because I only use subirrigation. And I hate using chemicals.

Lynnae,
I was told in a class a long time ago that once the nematodes eat all their prey ...... the have nothing left to exist on and they die off. That would be the need to add them again and again. And yes, when I did have weekly watered accounts the nematodes worked great.

Debbie

Lynnae,

The nematodes do a great job on the first application.

As mentioned, on problem accounts subsequent applications may be necessary.

These days whenever we get even a rumor of a fungus gnat we go and do a treatment to evety plant on the account.

As this is literally only a matter of putting a spoonful of vermiculite into each pot it only takes a few minutes.

The nematodes store well so it’s no big deal to have a suppl on hand for when you need them.

Fungus gnats are a thing of the past around here. Occasionally we will get them in a replacement plant or a new installation but that’s about it.

JK

Thanks for the info. guys. Which company ships the nematodes in a vermiculite bedding, John? And, I assume you are "topwatering" them in. What would you do in the case of a plant that didn’t need water that week?

Do you use yellow moniter cards for your problem accounts where you suspect re-occurence?

So glad you guys are getting great control. Could you imagine this business without it?

Hi Lynnae,

We use Greenspot:

www.greenmethods.com.

They sell pints of nematodes packed in vermiculite. (They say there are about 10 million nematodes in a pint...pretty crowded in there!).

We work the vermiculite into the soil a bit.

We haven’t had any problems with plants that don’t need to be watered. The nematodes would probably work a little better if you did water them in a bit though.

We do use yellow monitoring cards but for the most part, we actually use them to prove that the bugs people are complaining about aren’t coming from the plants!

Anyone ever hear of using an ammonia solution - maybe an ounce or so per gallon of water - to treat fungus gnats? One of my coworkers swears it works as well as Marathon.

Sheila, yikes! Ammonia. I wouldn’t recommend it, even IF there is some efficacy. Where do I start? First, its not labeled as a pesticide. Second, its relatively hazardous and smelly to handle on a large scale. Third, it carries a huge risk to affect your pH and possible burn your plants. Sorry, but I just wouldn’t use ammonia- there are too many other effective and safe solutions.

Also, Marathon for fungus gnats? The active ingredient, imidacloprid, works best on the basis of a piercing sucking insect ingesting the sap as the plant takes up the chemical systemically. It does have some efficacy as a contact spray, but is it even labeled for fungus gnats? I think also, merit is labeled for interior and marathon is an exterior product. I think you might want to check your labeling, too. Best of luck. Lynnae.

Marathon is labeled for interiorscape use, both the granular and water-mixed formulations, and carries a specific labeling for fungus gnat larvae. It works very well for gnats, but is probably the most expensive option and so, unless you’re treating for something else as a systemic, I wouldn’t waste the money when there are other products that are less costly.

Clem

Lynnae and Clem, Thanks!

We have had fairly good success with the DE. However, the time it takes for the adults to die seems like forever. It is suggested that when you have gnat situation that you should allow the soil to dry as much as possible and if you do have to water the water into the tray until the gnats are under control. I recently have had a horrible time of getting soil that does not produce gnats. I also recently heard of applying a mixture of 1 tablespoon pine sol per gallon of H20 for gnats. Ever heard of this? They are so annoying that I aim game to try it.

I wonder if the soil is particularly bad this year. Has it been stockpiled in hurricane-ravaged areas or something?

It seems like the gnats are an epidemic. Lots of clients have gnats in their personal plants, either on the job or at home, and I have had them on a couple of accounts recently.

Just subirrigate, and you will have the best of all possible worlds...check out this blog for great info on "the Cult of Subirrigation"...

http://www.insideplantslive.org/archives/cat_subirrigation.php

Adult gnats live up to 14 days or so, from the little I could glean in my own research on the subject. No matter the treatment, that’s something you’ll need to explain to your clients and ask them to bear with you until you have destroyed the gnats’ life cycle at the source, in the soil.

Clem

I’m confused!?